The parts to be processed are profiles that are required to be cut from large flat plates which require various types of processes to be performed on each part. Typically the part will require a process to sever a part profile from a parent plate but will also require machining operations such as drilling, tapping or milling. Typically the machining operations are performed prior to the profile being cut out to ensure the part is supported by a large portion of the plate during the machining operations.
Typically, on a profile cutting machine, such as with a thermal cutting machine, the bridge of the machine is often fitted with dry cutting tools such as laser, oxy fuel and plasma cutting torches and can also be fitted with high speed spindles for machining operations (wet cutting). Thermal cutting machines (laser, plasma and oxy fuel cutting) can produce waste such as dross (oxides and impurities) and smoke or fumes, while machining operations produce metal chips and may use coolant (eg oil and/or water) to assist in the machining operations.
Currently there are two different cutting table methods for a machine that combines multiple processes on one plate where there is thermal cutting and machining. The first cutting table method is a wet table type cutting system and the second is a dry table type cutting system.
The first cutting table method (wet type) is where the cutting machine operates over a cutting table that is full of water mixed with machining oil also known as coolant and this table has built in supports to support the parent plate during the various processes. This type of table is called a wet table type system as the cutting table is a bed of water and/or cutting oil mix. Usually the height of the water level is able to be raised or lowered to allow the water level to reach or cover the plate being processed.
When this table is used for machining operations the coolant in the cutting table is able to be recycled from the cutting table and back through the spindle, (generally after going through a filter). Additionally, the water in the table (from the cutting machine) can be used to minimise smoke and fumes caused during the plasma or oxy fuel processes.
The disadvantage of this wet table type system is because the cutting tables are large, there is a huge volume of coolant oil/water mix required to fill the cutting table. Additionally, during use of the cutting machines, because the plate is sitting over the coolant it can splash up so that the plates get covered with an oily residue from the oil in the coolant which can cause handling and other process difficulties necessitating extra cleaning.
Additionally, the cost to dump and replace the coolant/water mix is high
Additionally, because the fumes, molten metal and hot dross hits the water/coolant it creates steam mixed with wet metal particles which is free to escape into the atmosphere around the machine.
The second cutting table method (dry type) is where the cutting machine operates over a table with a fume extraction system to remove the fumes and smoke caused during plasma or oxy fuel cutting processes. This is commonly known as a dry table type system. The fume extraction system is located under the plate being processed such that the air below the plate is extracted complete with the fumes. These fumes are ducted to a filter system where the dust particles in the fumes are extracted from the air such that the air vacating the filters is clean. The filter materials used in these systems due to the volume of air being processed and the fine nature of the particles being removed, necessitates that the filter medium must remain dry to prevent blocking.
Currently when a dry type system including machining operations (such as drilling) are incorporated on this style of machine i.e. dry table type system, oil mist or very small amounts of coolant with air as a mist are applied to the machining operations so as not to cause problems with the filters.
The disadvantage of this system is that any coolant that has fallen below the plate being cut will be sucked into the filters when the fume extraction is turned on so the amount of coolant during machining is kept to a minimum to ensure the filters in the fume extraction system do not get wet. The low volume of coolant reduces the cutting tool life.
Additionally, another disadvantage of this dry table type machine combined with machining operations requiring coolant, is that there is no method to separate out the coolant from the fume extraction system so the amount of cooling that can be used is minimized as it cannot be recovered.
Additionally, other problems include reduced machining speed and tool life for the machining tools as they do not receive the ideal level of cooling and lubrication when using mist cooling.
Additionally, during machining operations such as drilling with mist cooling there is no coolant available to assist to push the metal chips up out of the hole as required for deep hole drilling and this can cause tool seizure in the hole or badly scoured surfaces in the hole.
Additionally, if the machine operators increase the coolant flow then any coolant will be limited to the amount that can sit on top of the plate, the rest will fall through holes and cuts and off the edge of the plate. This coolant as used in machining operations can fall through the table and be sucked up by the dry fume extraction system and cause the filters to block and need replacing.
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